#include <iostream>

using namespace std;

bool d[1000000000];

int main() {
  int l, r, m;
  cin >> l >> r >> m;
  for (int i = l; i <= r; ++i) {
    d[i % m] |= true;
  }

  int c = 0;
  for (int i = 0; i < 1000000000; ++i) {
    if (d[i]) c++;
  }
  cout << c << endl;
  return 0;
}